1. Field of the Invention
The invention pertains to a franking machine with at least one printing head of a printing mechanism for printing flat objects to be mailed such as letters, postcards, printed matter, etc., which can be either laid in or conducted through the machine, and with a guide arrangement, which is assigned to the print head and has a transport device, across which guide arrangement the objects to be mailed pass by the print head with their flat surfaces facing the printing mechanism.
2. Description of the Related Art
The machine in question is similar to the franking machines described in WO 01-62,503, WO 01-62,504, WO 01-62,505, and WO 01-62,506.
In addition to the standard rotary printing technique, new stamping application methods such as thermal and inkjet printing are also being used today for franking machines. It has been found in practice that especially the fussy inkjet technology reacts with great sensitivity to contamination in the area of the print head. This contamination arises primarily as a result of the dust particles which adhere to the transported objects to be mailed and which separate from the objects when they are laid in or transported through the franking machine. As a result, encrustations from on the print heads, which can interfere with the printing of the objects to be mailed to the point that the printed images or franking values become unusable or illegible.
Because such franking imprints often include barcodes, which serve to facilitate the automatic processing of the mail in mail distribution centers, the defects cited above often lead to significant costs. Because franking the same item a second time is unacceptable, inadequate franking imprints on the objects to be mailed must be reprocessed by hand, which takes a great deal of effort and leads to considerable expense.
The task of the present invention consists in designing a franking machine of the type indicated above so that it can always, that is, every time it is used, produce an imprint of uniform, high quality which is free of foreign influences, valid for its documentary purpose, and in conformity with postal requirements. In modern franking machines, inkjet technology is now being used more frequently. Special care must be taken in this case to prevent the dust carried along by the transported objects to be mailed from forming encrustations or from clogging the nozzles of the print heads. Dust also interferes with the quality of the imprints made by the other printing techniques as well, so that it is important to keep dust away from the machine in these cases as well.
According to the invention, the task described above is accomplished in that a suction device or a compressed air device is provided at least in the area near the printing head to act on the printing head in such a way as to keep it free of foreign dust-like materials, etc. It thus becomes possible to improve the reliability of the franking machine, to prolong the intervals between maintenance calls, and to maintain the good quality of the imprints.
The xe2x80x9carea near the printing headxe2x80x9d is intended to designate a suitable location in the immediate environment of the printing head where the suction air being carried away or the compressed air being supplied will not interfere with the proper functioning of the printing head. The use of suction air is more advantageous than that of compressed air, because the dust particles to be cleared away can be removed effectively in a current of air.
It has been found advisable for the suction air or compressed air transport device to have a blower installed in an air conduit, so that, as a result of the compact design, a space-saving arrangement can be obtained and/or the air conduit brought to an optimal point of the critical environment.
It has been found to be especially effective for the preferably nozzle-like end of the air conduit facing the area near the printing head to be located upstream of the printing head or of the printing mechanism with respect to the transport direction of the objects to be mailed.
In the case of a franking machine with a transport device operating with transport rolls rotating around axes arranged transversely to the transport direction of the objects to be mailed, it is advantageous for the end of the air conduit facing the area near the printing head to enclose at least partially a nonworking area of at least one transport roll located upstream of the printing head with respect to the transport direction of the objects to be mailed, through which the dust particles adhering to the transport roll or the paper dust separated from the objects can be carried away.
To the extent that space allows, it is effective for the end of the air conduit facing the area near the printing head to extend at least partially over the working width of the transport roll.
It is advisable for the end of the air conduit facing away from the area near the printing head to terminate outside the machine housing of the franking machine, so that the foreign materials being carried away can be disposed of simply, and thus no additional space is taken up inside the machine housing.
The end of the air conduit can in this case be designed as a collecting tank for the suctioned-out foreign materials.
To avoid the need for an additional drive motor, the blower can be connected to and driven by at least one of the driven transport rolls of the transport device.
To achieve higher rotational speeds than those of the transport rolls, a system of gears can be provided between the transport rolls and the blower to increase the rpm""s of the blower.
The invention will be explained in greater detail in the following on the basis of an exemplary embodiment with reference to the drawing, which should be consulted with respect to all details not explicitly mentioned in the specification: